2018

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GlideOffshore exploration by detection of hydrocarbon seepage

A large percentage of the world’s yet-to-find oil and gas resources lie under the seabed.Offshore exploration may be critical, but it poses major challenges: its high costs in particular make it difficult to carry out.That’s why it’s important to develop agile, selective technologies to locate promising emerging basins more efficiently, conquering this new offshore acreage cost-effectively.An example is the Glide project, in which a subsea glider equipped with special sensors detects natural hydrocarbon seepage in the water column.This innovation, a world first in the deep offshore, makes our exploration more efficient while cutting costs and HSE risks.

Though oil and gas are usually trapped in impermeable rock, small amounts still manage to migrate up to the seabed through the layers of the formation. Such seepage is a clear indicator that a possible active petroleum system is present.

A Disruptive Approach

Until now, the standard approach has been to use radar satellite images to identify oil and gas slicks on the water’s surface. But radar satellites cannot detect gas and oil dissolved deep below. The arrival of these gliders suitable for oil and gas exploration, developed by Total in partnership with French company ALSEAMAR, is a game changer.

The lightweight, autonomous submarines glide by means of small changes in their buoyancy, regulated by ballast. They move without a propulsion system, slowly and continuously gliding up and down the water column between the surface and a water depth of 1,000 meters. Ultra-light and unmanned, they’re guided by an onshore operator who transmits their navigation parameters. Highly energy-efficient, the gliders can operate autonomously for several weeks, without a supervising vessel, surfacing only to download their GPS coordinates and the scientific data collected via satellite.

This method of data acquisition, much less expensive, faster and safer than standard sampling techniques on ships, revolutionizes offshore exploration survey methods.

Specially Designed Sensors

The Glide project’s technological breakthrough consists of the sensitive onboard sensors. They can detect in situ, evaluate and observe natural hydrocarbon seepage from the seabed in real time.

Developed by Franatech, the METS sensor offers highly sensitive methane detection and fast reaction times: up to 20 nmol/liter, in a few seconds.

Research is being conducted to add new sensors to the glider. Candidates include a carbon dioxide sensor for exploration applications (differentiating thermogenic and biogenic gas) or monitoring offshore carbon storage reservoirs; an acoustic sensor that could detect the sound of hydrocarbon plumes in the water column; and a Doppler speed sensor to measure ocean currents. Another long-term possibility is doing direct sampling at the source of the seeps.

Gliders preparation and calibration before deployment

Glider deployment

Awaiting for navigation orders after data transmission

Diving for natural hydrocarbon detection

Natural hydrocarbon detection in progress

A Bright Future

Several tests of these gliders in real-world conditions have already established their ability to detect natural hydrocarbon seeps in water. After an initial evaluation test off Cyprus in 2015, a demonstration pilot was conducted in Angola’s deep offshore Block 32 in November 2017. The 20-day trial was combined with simultaneous acquisition of radar satellite images. It was a resounding success. The vertical movement of hydrocarbon fluids toward the surface detected by the gliders perfectly matched the active seep site locations seen by satellite. Over the same period and in partnership with ALSEAMAR, we confirmed the detection of methane, whose plumes had been identified earlier by ocean research institute IFREMER using multibeam sounders in the Bay of Biscay.

But the adventure has only just begun: new subsea gliders are in development for water depths of 2,500, then 6,000 meters in the next decade. And there are potential environmental applications associated with our activities.